Obesity is reported to be the commonest nutritional disorder in Western societies (Zhang, Y. et al. (1994)) More than three in 10 adult Americans weigh at least 20% in excess of their ideal weight (Zhang, Y. et al (1994)). Increased body weight is a public health problem because it is associated with important medical morbidities such as type II diabetes mellitus (i.e., non-insulin-dependent diabetes mellitus), hypertension and hyperlipidaemia (Grundy, S. M. & Barnett (1990)). There is evidence that body weight is physiologically regulated and the obesity (and its related conditions or diseases) are due in part to derangements in this regulation (Zhang, Y. et al. (1994)).
In rodents, there are described seven single gene mutations that result in an obese phenotype; five of which are present in mice. Of these seven rodent models, one of the most intensively studied is the obese (ob) gene mutation in mice, identified in 1950 (Ingalls, A. M. et al. (1950)). Mice homozygous for this ob gene mutation are profoundly obese, develop type II diabetes mellitus, and are hyperphagic and hypometabolic, as part of a syndrome resembling morbid obesity in man (Friedman J. M. et al. (1991)). This ob gene is mapped to the mouse proximal chromosome 6 and encodes a protein (i.e., ob protein) expressed in adipose tissue (Zhang, et al. (1994)). Mice homozygous for the ob gene mutation have little to no production of this ob protein, and accordingly have defective regulation of body weight leading to obesity.
The murine or human ob proteins may be administered to patients suffering from defects or mutations in their corresponding obese (ob) gene, which defects or mutations prevent or interfere with the production and/or function of the ob proteins in modulating body weight. These proteins may therefore be used as a hormone-like substance to control, prevent or treat obesity and its related diseases and conditions in man and animals.
To use the murine or human ob proteins in this manner, these proteins can be administered through injection by a variety of routes, such as intraperitoneal, intravenously, intramuscularly or subcutaneously, in frequent dosages. Since it is administered frequently through injection, it is important that the murine or human ob proteins be purified, preferably to homogeneity, be free of contaminating protein materials, and be recombinantly expressed in a soluble and biologically active form. It is generally known to practitioners in the field that contaminants present in injectable medication can often lead to toxic side-effects or adverse immunological responses.
While the murine ob gene sequence is disclosed in Zhang, et al (1994), no methods of expressing the murine ob protein or its human counterpart have been reported, much less producing these proteins in a biologically active and soluble state from which the proteins can be purified to homogeneity. Therefore it is important, and is an object of this invention, to express and produce the murine or human ob proteins in a homogeneous, soluble, and biologically-active state.